Testing of online components, such as websites, website features, web services, online applications, and the like, is typically carried out to ensure that the online components function in an expected manner. As one example, testing may verify that an online component performs as intended when interacting with various combinations of web browsers and operating systems, other online applications, and so forth. As another example, testing may include stress testing to determine how an online component performs under load from a large number of users. In general, most developers do not possess the capability to perform comprehensive testing of online components. Accordingly, testing software or a testing service may sometimes be employed to perform some testing of the online components.